Testing ElarmS in Japan

Abstract

Earthquake early warning systems use seismic networks, rapid telemetry, and software algorithms to detect an earthquake immediately after its inception, estimate its damage potential, and disseminate a warning to surrounding communities before peak ground shaking occurs. Earthquake Alarm Systems, or ElarmS, is an earthquake early warning system developed in California. The ElarmS algorithm recognizes earthquakes from the initial P -wave arrivals at seismometers near the epicenter. The characteristics of the P wave, including amplitude and frequency, are used to estimate a final magnitude for the event. P -wave arrival times from several stations are combined to estimate the hypocenter of the event. Finally, the estimated magnitude and hypocenter are applied to attenuation relations to produce a prediction of ground shaking levels in the region. ElarmS has been tested extensively with datasets of earthquakes from northern and southern California (Allen and Kanamori 2003; Allen 2007; Wurman et al. 2007; Tsang et al. 2007; Allen et al. 2009). While the test datasets from California included a large range of locations and source types, there are a limited number of recent, well-recorded, large earthquakes available for testing the early warning system. In this study we take ElarmS to another geographic and seismic setting and test the algorithms with a dataset of 84 large-magnitude earthquakes, including 43 of magnitude 6.0 or greater, in Japan. The Japanese test dataset is valuable both for the insight into ElarmS' processing of large events and for the chance to process events in a completely different geologic setting. The offshore and deep nature of many of the events presents new challenges to the methodology. The Japanese earthquakes offer an opportunity to improve the robustness of ElarmS, extend its abilities to other settings, and confirm its relevance for large-magnitude events. The dataset contains 84 earthquakes recorded …